Mutations in the amyloid precursor protein (APP, located at chromosome region 21q21.2) (43), presenilin 1, (PSEN1, located at 14q24.3) (44), and presenilin 2 (PSEN2, located at 1q42.13) (45) are well known to cause early onset AD. The gene discussed is PSEN2; the disease is Alzheimer disease.